This loop should subtract one off the r value, but it's not, It just makes it yellow and breaks
for i = 255,0,-1 do script.Parent.TextColor3 = Color3.new(i,255,0) wait(.1) end
Try this instead.
for i = 255,0,-1 do script.Parent.TextColor3 = Color3.new(i/255, 1, 0) -- 255/255 == 1 wait(.1) end
Color3 constituents uses numbers from 0 to 1 and anything in between. That's why I divided i
by 255.